Process for discontinuously physically developing latent photographic images



'fication 439,005)

Patented Sept. 2, 1952 PROCESS FOR DISCONTINUOUSLY PHYSLC I CALLY DEVELOPING LATENT more.- I PHIC IMAGES Roelof Jan Hendrik Alink, Cornelis Johannes Dippel, and Harke Jan Houtman, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Conn., as,

trustee No Drawing. Application October 8, 1948, Serial 1 6 Claims. 1

The invention relates to a method of producing contrasts, consisting of metal, in photographic materialby physical development of latent images in sensitized, lyophilicf supports, the term physical development being understood to mean a method of developing according to which, prior to' development, all the metal required for building up the contrast does not yet occupy itsposition inthe contrast as an ion or as a compound and the term latent image being understood to mean the image which is produced by mere exposure of. the photographic material before external measures are taken to intensify this image; in some cases the said image may already be visible.

.f This physical development is :carried out with Ithe use of a metal compound adapted to be reduced to metal in an aqueous solution, such as a salt of mercury, silver, gold or platinum, and of r a reducing agent. By way of example may be mentioned here the development to form a silver image of a latent mercury image produced by I and contaminate and in addition metal is liable to be deposited. during the developing process even at unexposed areas of the light-sensitive layer, which may result in fogging.

. These difficulties are such that hitherto such a physical development, without the laboratory, has never been carried outron an industrialiscale.

-. The methods hitherto suggested invariably amount to bringing the photographic material into contact with a supply of fresh developer,

which has become unserviceable at the end of the development, considerable contamination generally occurring due to metal being separated out of the solution. It is true that it is possible to produce developers which are comparatively stable according to the standards applying for physical development, but the stabilisation, also results in a deceleration of the development, so

that for most purposes the latter proceeds excessively slowly, whilst at the same time the stabilized developer can only be used on one occasion. It should be noted that technical use of physical development is attractive. For definite kinds of photographic material (vide, for example, the above-mentioned British patent specitreatment is even confined In the Netherlands October 27-,

thereto. In other cases physical development is desired from considerations of the quality of the image, for example, in view of the high resolving power which can be obtainedtherewith. However, in the technical use of physical development the problem-arisesas to how large quantities of photographic materialare to be readily worked up and how waste of chemicals is to be avoided as far as possible. For-this'purpose efforts may be made, for example, -tocarry out physical development as a continuous process or, as an alternative, tosolve thep r o'blem', while maintaining the discontinuous nature of physical development. For strip-like photographic material such an effort resulted in the methoddescribe'd in the British 7 patent specification 545,901, according to which a large length of 'suchm'a'te'rial 'is wound on a drumv and is treated with a restricted quantity of physical developer. The present invention provide a solution of the same problem, which solution permits of-satisfyingacompletely different need out vof "practice, that is to say physical development of. large numbers of sheets of photographic material. It often occurs, for example, that photostat copies of printed texts are required to be made' Attempts could be made to designa continuously operating machine for this purpose. However, such a machine requires regular supply of photographic material and when in use presents the difficulties attendant on the use of continuous physical development, that is to say the problem of avoiding soiling and that of refreshing the developer. On the other hand'discontinuous physical development is unserviceable'.here'without further expedients: fresh developer is required'to be made at intervals considerable supervisionis needed,

the production is excessively small and thewaste of chemicals in the exhausted 1 developer is excessive. The invention has for its object to obviate these latter difficulties.

According to the"invention, 1yophilic photographic material in the form of a pile of sheets is developed in a stable physical slow-action developer which contains not more than approximately three times the'quantity of metal salt which just suflices for building up the contrasts.

For measuring an exactly suitable quantity of the preparation, that is to say after mixing the solution of the'metal salt and the solution of the reduction agent, visible separation of metal in the liquid has not yet occurred. The times of development in such stable physical developers are generally also at least minutes. Long times of development have the advantage that the duration of development is not particularly important so that less supervision is required during development. If moreover use is not made in such a developer of considerably more metal salt than is suflicient for building up the contrasts, it is only thi small excess of metal salt which may result in deposition of metal at undue, that is unexposed areas in the photographic material, or in other words fogging, and in the liquid, or in other words soiling. It is surprising that even if, owing to these measures, the con centration of the metal salt is materially reduced, the rate of developing generally does not become inadmissibly small and that nevertheless the imagesbecomesufficiently black, so that a favourable ratio between the quantity of metal taking "part in'the productionoi the image and the waste of metal is ensured. I On the contrary, material reduction of the concentration of the reducing agent exerts adetrimental effect both on the rate of developing and'on'the blackening. The use of a quantity or metal salt slightly in excess of the quantity'just sufficient for building up the contrasts has a further advantage in that the metal salt which-is usually the most expensive constituentof the physical developer, is utilized If use is'madeof: physical development accord- I mg to the invention,little'supervision is needed 'and afterdevelopment the piled material may be left in the developing liquid for a considerable time. This time maybe longer according as the excess of metal salt contained in the developer over I the "quantity joi metal salt which is just fsuiiicientfor buliding up thec'ontrasts is smaller. Ift'his excess is notjhigher'than 100% 'the' time during which thelpiledmaterial sojourns in the developing liquid is unimportant so long as it is lsuificient. A sojournyfor example, for a whole night, even if thej development occurs in a con- ;siderably shortenperiod, for example half an "hour, is not inconvenient. fit is to be noted that ,i n' the'case of suchalong sojourn of the photographic material in the developing liquids foggingor production of" stains was never observed,

.as is the case with chemical development of 'lfongl'duration orf off piledquantitiesof, for ex- "aniple, silverbromide paper. 'In view ofjthese considerations -it fis obvious that, j according to the'invention, 'usejjispreferably'made of a de- 'veiopm liquid which" contains not more than produced werealwaysof 's atisfactoryuuality with 'sufficient blackening and free from fogging and If the support of j thefphotographic material readily allows the passage of the developing liquid, as in the case, for example with an aqueous developing liquid, of regenerated cellulose and of paper'notfglued intensely or not glued at all, such; forexampleas most kinds of base generally necessitates taking special measures Thus, for example, the sheets of photographic material may be introduced into the developing liquid one at a time and piled up therein, so that'- irom the start a layer of developing liquid is provided between each pair of consecutive sheets,

excellent results being thus obtained. The same result, that is to say suificiently rapid moistening of the sheets of paper may, however, be obtained by adding to the developer a given quantity of a diffusing agent and for this purpose use may be made with satisfactory result, for example, of the product delivered on sale by the Imperial Chemical Industries under the registered trademark of Lissapol-N,. The latter is a wetting agent or detergent which has been described in a paper entitled fWetting and Detergency issued in 1937 by the Chemical Society of London and is a polyether aswell as a monohydric alcohol having the probable chemical formula:

The quantity required varies with the content of glue in the paper and is generally from some few tenths of a percent to some few percents in the developer. Other diffusing-agents are also suitable if they do not result in undue reactions with the developer or the chemicals in the photographic material.

At the moment when the'developed pile is removed from the developing bath, the developer is generally exhausted. As already mentioned, it is common' practice to use developers having a plentiful proportion of reducing agent compared with their content of metal salt, because such developers yield better results in practice and in addition the reducing agent is almost invariably cheaper than metalsalt. Such developers are exhausted as soo'n'as the metal salt is consumed and converted into metal which has served for the formation of the image and may have deposited in part without the photographic material. The remaining solution may still contain a considerable quantity of reducer and-may be used to prepare a, fresh developer by adding a measured quantity of metal salt, preferably in the form of a concentrated solution. The developer thus 'regenerated'allows of being used again. It should be noted'in addition that'with the stabilized developers specifically used according to'the invention contamination due to'oxidation by atmospheric oxygenis of no importance in practice.

The aforesaid stabilized developers may be 'produced in various ways. 'A customary physical developer contains 1 'or 2% of metol or hydroquinone to which an organic acid, say citric acid or tartaric acid, is fad'ded to adjust the pH to approximately 2 This solution provided with, for example, 0.5% of silver nitrate, developes,

within a 'few' minutesa" latent image so as to form a silver image and is exhausted in about 10 minutes owing'to themetal salt being reduced completely to "metal. Such developers allow of being'stabilized by diluting them withfsay, a 25-fold quantity of water, so that "the concentration of the reducing agent has a molarity of not more than 0.01 or by'reducing the pI-l'to a value of less than 1, for example of about 0.5,

with the use of a strong acid, for example'nitric The definition, blackening and effectiveness a i or else by cooling' them with the addition ,of glycerol or the like, if necessary, to a temperature lower than C., for example 0? C. or even lower. The time of development thus becomes at least minutes. If care is takento see that the quantity of metal salt does not appleoiably exceed; the quantity just-required for developing the pile concerned, the pile m ay be allowedto stand overnight in the developer without objection, without entailing foggingor soiling. After the pile has been removed from the developer, metal salt may again be added to the developing liquid and anotherpile may be developed therein, as above described.

It-often occurs that among the photographic material to be developed there are one or more sheets, or even a whole pile, which are required to be rapidly developed. In accordance-with a particular embodiment of the invention, this may be achieved by the phot ographic material to be rapidly developed, without the pile being subjected sheet by sheet to direct radiation, preferably by infra-red light, and the outer sheet,eac h tim'e' its developmentis completed, being taken from the jpile and removed from the developer.

' The 'infr'a-red rays are substantially absorbed by the sheet on the outsideof the pile and more "particularly" by the image already partially .pr'oduced.

Di]. the development of the material required jtdb e' rapidly developed being completed, any rejirlainder of the pile may be subjected, without radiation, to the action of'the developer.

0 Example I Q 30 foils (size 9 x 12 cms.) of regenerated cellulose'were sensitized with a solution of- 0.1 -n hydroxy-l diazonium-Z methyl-6 benzene 'sulphonic acid-4, 0.035 n mercurous nitrate and 0.05 n nitric acid; after drying they were exposed, in con- =tact with a photographic negative, for 80 seconds at a distance of 15 cms. with the use-of a high-pressure mercury-vapour discharge lamp of -500 w. The foils were then piled and the pile formed was'put into 250 cc. of a dilutephysical- "developer containing 0.05%"of metol, 0.01% of tartaric acid and 0.02% of silver nitrate, the 'prints being left'therein for about 6 to 8 hours and being finally washed in water and dried.

The contrasts obtained were sharply defined and effective and showed no fogging.

Example II 25 sheets of heavily glued paper (size 9 x 12 cms.) were sensitized by immersion in the sensitizing solution referred to in Example I. Subse-- .quent to drying they were exposed, in contact with a photographic negative of a printed text, fore-3 seconds at a distance of 25 cms. from ahigh-pressure mercury-vapour discharge lamp of .500 w. a The sheets were then piled in a developing dish containing 125 cc. of dilute physical denight.

A similar result was obtained by developing for 15 minutes or more in an equal volume of a di- 6 rlute .physical "developerc tai n 0.05%v .oi.;h$"- droquinone, 0.02% of silver nitrate. Foggingdid not occur. j

Example III I V sheets of'basepaperfor phototype (80 'grs. persquare metre), 9x 12 aris -sensitized by twosided application, by rolling, of a'solution of 0.4 n hydroxy-l diazonium-2 methyl-6 benzene sulphonic acid-4, 0.4 n mercurous nitrate and 0.4 n .nitric. acid, were exposed on both sides in contact with a photographic negative of. av printed text, then piled uppand introduced all of them atthe same time, in the form of a pile, into 250 cc.of;a dilutephysical developer of thefollowing composi tion: 0.1% of metol, 0.2% of; tartaric acid, 0.04% of silver nitrate, everythingin water.

After 45 minutes or more the pile was: taken out of the. liquid. After washing and drying,;the copies were found to be 10f satisfactory quality, whilst a vdifference between the outermost and the innermost sheets of the pile could not be: ascertained. I

"Example IV 25 sheets of base 'paper for phototype, sensitized in the manner described in Example IIIand exposed, were jcombined to form apile" andithis pile wasimmersed, as a whole, in cc. of a strong-acid ,physicalfdevelopercontaining 1% of metol, 0.3 n" nitric' acid, 0.02% of 'silver nitrate, everything in water, and developed. The development of the pile was completed in about 15 minutes and the result was the same as mentioned in the preceding examples, eve'nwhen the pile was left tostand for a longer period in the developingliquid. When not used. this develop- .er remains'stab'lefor a' few hours. It may be regenerated by adding 2.5 cc.'of a solution of 1% silvernitrate in water.

Example V 2 5-sheets of unglued paper were sensitized in the manner described in Example III dried and unilaterally exposed in the above-mentioned manner. They were combined to form a pile and the pile was immersed in a developer of the composition: 0.l% of metol, 0.2% of tartaric acid, 0.2% ofsilver nitrate, everything in water..

. The quantity of developer was 5 cc; per square dm. of paper to be developed.

After a sojourn of 75-minutes in the developer and subsequent to washing and drying .01 the sheets, the contrasts in all thesheets of the pile were found to be excellent.

. mple v1 25 sheets of paper, sensitized and exposed in the manner described in Example III were combined toform a pile and immersed-as such, in a developing tank containing 250 cc. of a developer of the following composition: 1% of hydroquinone, 4% of tartaric acid, 25% of glycerol, 0.02% of silver nitrate, everything in water.

By cooling this developer was kept at a temperature between --6' and 3 C. After two hours the pile was removed and the sheets were washer and dried. Thequ'ality of the contrasts is satisfactory. The sojourn of the pile in the liquid may be prolonged at will. The developer 'may be regenerated by adding 2.500. of a solution of 1% silver nitrate in water to the exhausted developing liquid. Soiling and fogging donotoccur. I N r Y developer-gmaybe'usedto develop-at room temperature, the -time -of development heing about 4 minutes. In this-case it is necessary for the photographiematmialto be removed fromv .addingta: fresh supply oisilver nitrate.

. E a ple, v11

25"'sheets of base =-paper;'for I phototype were sensitized and exposed in the mannerdescribed in Example In. The sheets were piled up in adev'eloper-ofthe compositionmentionedinExample Viand: this in such manneri that a thin li'quid layer only covered the pile. Afte1'-the pile had been standing for 5 minutes :inxthe developer an-infrared' radiator (Philips-Heliofluxj 500 w.) was ignitedat Swims. above the liquid surface. Aiter Jsuflic'ient development, the topmost sheet was removed each timefrom the pile, washed and dried; After'5 minutes, ten satisfactorily developed sheets were removed from the pile. Without radiation, at least'45 minutes are required for development.

' Example VIII .i'ac's eetsgof heavily gluedpaper"(9 x .12 ms.)

' were "mechanically provided with .a solution ofthe "following composition: 0,4 nihydroxy l fdiaZO- mum-2 methyl-obenzene,sulphonic acid-0. 1 n mercurous nitrate 'andOA n nitric acid. 7;,Ifhey wergthen dried and exposed incontact with a photographic negative of a printed textfior v25 *seconds at a distance of 40 cms. from awatercooled high-pressur mercury-vapour. discharge lamp of 500 W. The sheetswere put in the form of a; pilein a developing dish containing 50 cc. of adeveloper of the following composition; 0.1% of metol, 0.2% of tartaric acid and 0.02% of silver nitrate in water. After 30 minutes the pile was removed from the developer, after which the sheets were washed in water for 30 minutes and then dried. The outermost sheetsof the pile were satisfactorily developed, Whereas the innermost sheetsybut for th edges, weredeveloped very ini completely only.

:"Onintroduction, on the contrary, of" a similar pile of.: sheets of heavily glued paper into 50cc. of the same .ldeveloper which: contained in addition 4% of'the diffusingagent Lissapolt" above referred to, it was found-that after alapse of time of .3osminutes'all the sheets:were developed so as ,to exhibit satisfactory" blackening.

.'What we claim is:

1. A method of producing photographic metal contrasts which comprises stacking a plurality of sheets of photographic material each of which ,,comprises a lyophilic support carrying-a lightsensitive system containing :a: diazonium compound rand.a-mercurous salt and which ,hasbeen .exposed to lightxto form aqlatentphotographic .contrast thereon ,in astable developing *liquid .-..containin a metal saltreducible to-a metal in solution anda compound capable of reducin the metal salt toa metal, said liquidcontaining a quantity or said .metal-salnwhichis insu-iiicient amount to completelyedevelop the said latent contrasts-in all the sheets but'which is less than three times said amount forta timesufi'icientsto completely develop thesaid latent-contrasts.

2. A et od- :oi p ducin photo aph c metal @contrastswhi'ch comprisesstacking a-plurality of sheets ofphotographicmaterial each ofiwhich comprises a lyophilic support carryingazlightsensitive System containing a diazonium compound and-a mercurous 'salt and which has been exposedto light to form alatent photographic contrast therein,- and introducing a said stack of 7 sheets intoa stable developing liquid containing a metal salt reducible to 'ajmetal in solution, a compound capable-of reducing the metal salt to a metal, and a diitusing agent, said liquid containing a ouantity-ofsaid metalsalt which is in *suflicient-amount to completely develop the said latent contrast but less than three times the said amount for a time sufficient to completelydevelop the said contrasts.

3. A method of producing photographic metal contrastswhich comprises stacking a plurality of 7 sheets of photographic "material each ofwhich comprises a lyophilic-support carrying alightsensitive system containing *a diazonium compound and a; mercurous salt and which has been exposed to light to' forme latent photographic contrast thereonin a stablev developing "liquid containing a metal salt reducible to a, metal, in solutionand a compound capable of reducing the metal salt to a metal, said liquidgcontaining a quantity of said'metal salt-which is insufficient amount to completely develop the, said latentcontrasts but less than three times said amount for a time sufficient to completely develop the said latent contrasts, exposing the top sheet ofsaid hasten development of the same, and removing stack in'said solutionto infra-red radiation to 1 the top sheet to expose the underlying sheetto the infra-red radiation.

4. A method of producing photographic metal contrasts which comprises stacking a plurality of .sheets of photographic material each of which comprises --a-ly0phi1ic support carrying; a lightsensitivesystem containinga diazonium compound-and a. mercurous salt and which hasbeen exposed to light toform a latent; photographic .scontrast gthereon in astable developing liquid having apH-lessthanl and; containing a metal salt reducible to a metal in'solution and a compound capable-of reducing themetal salt to'a metal saidwliquid containing a quantityof said 5 metal salt which is insufficient-amount to com- ,pletely develop thesaid latent contrasts but-less .than three times: said -a-mount fora time suffi- :cient to completely develop. the-said latent .contrasts.

5. A method of producin photographic-metal contrasts which comprises stacking a plurality of sheets of photographic'material each of which comprises a lyophilic support carrying a lightsensitive systemeontaining a -diazonium com- :pound and-a mercuroussalt and-which has been exposed to light-to form a latent photographic :contrast thereon in a stable developing liquid containingametal saltlreducible-to a metal insolutionuandilessthan 0.01 molar amount of-a compound capable of reducing the metal salt to a netal,..-saidi liquid containingxa quantity of said metal-salt which. isin .sumcient-amount to completely develop the. said latent contrasts but less than three times said amount for a time suificient :torcompletely develop the said latent contrasts.

::6.;'A-;method of producing photographic metal contrasts which comprises stacking a plurality of sheets of photographic material each of'which comprises a lyophilicssupportcarrying a light- ..sensitive: system containing a diazoniumpompound and amercurous saltand which hasheen exposed to light to form a latent photographic contrast thereon .inta stable developingliquid at .'a temperature lower than 10C. and containing a. metal salt reducible to a metal in solution and a compound capable of reducing the metal salt to a metal, said liquid containing a quantity of said metal salt which is in sufiicient amount to completely develop the said latent contrasts but which is less than three times said amount for a time suflicient to completely develop the said latent contrasts.

ROELOF JAN HENDRIK ALINK.

CORNELIS JOHANNES DIPPEL HARKE JAN HOUTMAN.

REFERENCES CITED The following references are of record in the file of this patent:

OTHER REFERENCES Clerc, Photography Theory and Practice, pub- 15 lished by Sir Isaac Pitman Ltd, New York, N. Y.

(1937), pages 268 and 269. 

1. A METHOD OF PRODUCING PHOTOGRAPHIC METAL CONTRASTS WHICH COMPRISES STACKING A PLURALITY OF SHEETS OF PHOTOGRAPHIC MATERIAL EACH OF WHICH COMPRISES A LYOPHILIC SUPPORT CARRYING A LIGHTSENSITIVE SYSTEM CONTAINING A DIAZONIUM COMPOUND AND A MERCUROUS SALT AND WHICH HAS BEEN EXPOSED TO LIGHT TO FORM A LATENT PHOTOGRAPHIC CONTRAST THEREON IN A STABLE DEVELOPING LIQUID CONTAINING A METAL SALT REDUCIBLE TO A METAL IN SOLUTION AND A COMPOUND CAPABLE TO REDUCING THE METAL SALT TO A METAL, SAID LIQUID CONTAINING A QUANTITY OF SAID METAL SALT WHICH IS IN SUFFICIENT AMOUNT TO COMPLETELY DEVELOP THE SAID LATENT CONTRASTS IN ALL THE SHEETS BUT WHICH IS LESS THAN THREE TIMES SAID AMOUNT FOR A TIME SUFFICIENT TO COMPLETELY DEVELOP THE SAID LATENT CONTRASTS. 